On 20 December last year, Spain went to the polls in what turned out to be a historic general elecion. After the votes were counted, it appeared that the governing centre-right Popular Party had won 28 per cent of the vote, and the old establishment Socialist Party 22 per cent; but almost as many votes – just under 21 per cent – had been won by Podemos, a new party of the anti-austerity left launched barely 18 months ago.

At a stroke, in other words, voters had chosen to bring an end to the steady alternation between Popular and Socialist governments that had dominated Spanish politics since Franco’s death 1975; and although coalition negotiations are proceeding at a snail’s pace, there are now, under Spain’s proportional election system, three major parties in Spain’s national parliament, each of roughly equal size.

And we in the UK could do worse than to take a look at that Spanish result, as we struggle to understand what is going on in our own politics; for ever since Jeremy Corbyn was elected Labour leader four months ago – and particularly since that huge crossbench roar of approval that greeted Hilary Benn’s speech on Syria last month – it has been clear that tectonic plates are on the move, at a speed to rival a melting Greenland glacier.

If there’s one truth that seems to be written into the DNA of British politics, after all, it’s that it revolves around a two-party system; in 1882, Gilbert and Sullivan even satirised the whole structure, pondering in their comic opera Iolanthe why it was that “every boy and every gal, that’s born into the world alive, is either a little Liberal, or else a little Conservative!”

And even after the First World War, when the Liberals largely dwindled away to be replaced by the Labour Party, the two-party structure enshrined in the architecture of the House of Commons remained intact. People belonged either to the left, which spoke for the masses, or to the right, which spoke for privilege and property; and to all superficial intents and purposes, that system still prevails today.

The only problem is this; that the divide down the centre of the House of Commons no longer embodies the deepest ideological divide in the Chamber, which these days runs straight through the middle of the Labour Party, split as it is between serious dissidents from the austerity narrative sold to the British people since 2008 – who are also, in the main, critics of the model of capitalism currently operating in the UK – and those who largely accept the current system, but wish to ameliorate some of its impacts, and are therefore ideologically closer to the Liberal Democrats, and to the liberal (and more pro-European) wing of the Tory Party.

As in Spain, in other words, we have developed a politics dominated by a large, bland, besuited middle with a fairly boring establishment face, flanked on either side by a more radical social-democratic left, and a more chauvinistic and nostalgic right; and the same truth, in a slightly different form, prevails in Scotland, where despite its anti-austerity rhetoric, the dominant SNP always dresses smartly, tries to be all things to most people, and, in policy terms, often fails to inspire.

The difficulty for the UK, though, is that unlike Scotland and Spain, Westminster has an electoral system which demands a binary response, and is thrown into near-chaos by this kind of ideological shift. The truth is that as New Labour and moderate Tories drew closer together in ideological terms over the last 20 years, Westminster and its attendant groups of commentators became used to a system in which the two main parties bickered over an increasingly narrow range of policy detail, while never questioning the big founding assumptions on which their policies were based: the primacy of markets, for example, or the protection and promotion of Britain’s main export industries – including an increasingly dysfunctional financial services sector, and an arms industry with a questionable client list.

And it’s therefore difficult to overstate the profound shock to those involved in this structure – and convinced that it represents all the democracy we need – of finding that one of its main elements has suddenly slipped into the control of another group, the long-banished and marginalised left of the Labour Party.

If all those career politicians at Westminster and Holyrood were genuinely interested in politics, of course, they would already – in response – have moved far beyond the current round of personal attacks on Jeremy Corbyn. They would be asking why the three establishment candidates for the Labour leadership were so poor, and why Jeremy Corbyn defeated them so convincingly. They would be asking exactly why Scottish voters delivered a first-past-the-post SNP landslide in last year’s general election. And they would be asking how the bulk of their party’s MPs came to share so much ideological ground with the Tories, and whether that historic move to the right remains a good electoral strategy, or one that should now be avoided, on basic grounds of integrity and common sense.

Instead, though, all we can hear at the moment is the outrage of a section of the elite that was used to having complete control of its Westminster world, and has now had to cede at least some of that control to a hated left-wing enemy they thought they had defeated for good. They’re throwing their toys out of the pram, behaving atrociously, and using their many friends in the media and on the Tory benches to amplify their long whine of entitlement and outrage at the cheek of the Labour membership in electing the “wrong” leader.

Yet none of these petty and personalised responses will heal the profound breach that now runs through their party, and through much of west European politics. For that process would require the kind of political vision and creativity that this mediocre generation of centrist politicians so profoundy lacks: either the intellectual fire-power to reinvent a form of 21st century social democracy that could actually encompass both Jeremy Corbyn and Hilary Benn – or the courage to recognise the end of one political story when it comes, and the need, even in a fiercely hostile electoral system, to begin another, from scratch.